1. Field of Invention
This invention is directed to systems and methods for detecting streaks, such as streaks caused by imperfections in scanning systems that employ linear imaging arrays.
2. Description of Related Art
A variety of systems and methods are conventionally used in digital scanning. Typical scanning systems employ imaging arrays that are stationary with respect to the devices in which they are housed, or which are caused to move relative to a stationary substrate to be scanned. In such systems, constant or variable rate movement is effected between the image to be scanned and the imaging array. The imaging array takes a rapidly sequential series of pictures of the image medium that is presented to be scanned as the relative movement is effected. The scanning system then digitizes the image scanned for storage and/or reproduction.
A difficulty in such systems is that any imperfection in the field of view of the imaging array is repeatedly scanned and digitized. The result is that the reproduced output image from the device will include a streak or line corresponding with the position of the imperfection.
Various exemplary scanning devices employ stationary Full-Width Imager Arrays (FWA) or linear Charge-Coupled Device (CCD) arrays. In such systems in which the imaging arrays are stationary, the arrays are often separated from the image to be scanned by a platen glass or other transparent surface or lens overlying the imaging array. Various exemplary methods are employed in these devices to move the image across the transparent surface. One such exemplary method, commonly referred to as Constant Velocity Transport (CVT) scanning, employs a belt, drum or other like device to move the image substrate to be scanned across a linear sensor, such as, for example, an FWA.
A recognized problem in imaging array scanning systems, such as, for example, CVT scanning devices, occurs when dirt particles, contaminants, imperfections, obstructions and/or other objects appear on the transparent surface, or otherwise in the field of view of the FWA or CCD. Such dirt particle, contaminant, imperfection, obstruction and/or other object remaining stationary on the transparent surface, or otherwise in the field of view over the FWA or CCD, is repeatedly imaged and digitized as though it were part of the scanned image. The result is that the image reproduced by the exemplary CVT scanning device will include a streak or a line on the subsequently reproduced image.
A variety of systems and methods are employed to ensure that the platen glass is kept free of dirt particles, contaminants, imperfections, obstructions and/or other objects. These systems and methods thereby improve reproduced image quality. Many of these methods are manual, requiring visual inspection and manual cleaning of an exemplary system's platen glass. Other systems and methods for improving reproduced output image quality include automated system steps which review the reproduced output image in comparison with the scanned image in order to detect and compensate for differences before the reproduced image is displayed. One complication with this approach is that it is difficult to determine whether a line which is digitized and reproduced as part of the output image is actually part of the image that was scanned or whether it was produced because the FWA or CCD repeatedly scanned any imperfection, stationary in its field of view, and then reproduced it as a line or streak in the reproduced image.
Difficulties in detecting dirt particles, contaminants, imperfections, obstructions and/or other objects are particularly acute as those which commonly produce streaks in conventional and exemplary CVT scanning systems are extremely small. Any dirt particle, contaminant, imperfection, obstruction and/or other object generally large enough to be detected by simple visual inspection is, in general, large enough to be picked up by the scanned image substrate as the scanned image substrate is moved across the platen glass. The dirt particle, contaminant, imperfection, obstruction and/or other object is moved out of the way, swept away with the movement of the substrate being scanned. Dirt particles, contaminants, imperfections, obstructions and/or other objects that are very small, on the other hand, have a greater tendency to adhere more to a platen glass and to resist being swept away by the movement of the image substrate.
Among the systems and methods employed to remove streaks from digital images produced in CVT scanning systems, software algorithms exist that review the stored data which represents an entire scanned image. Such software algorithms apply revisions before reproducing the image on an output display device. A disadvantage in such methods is that full image review algorithms require the scanning of the entire image and storage of the data representing the scanned image before reviewing the data in its entirety and applying necessary revisions. In high speed scanning applications, this requirement to record an entire image and then review and revise that image before reproducing the image has the potential to slow the scanning and reproduction process to an unacceptable level.